The long term objective of this proposal is to elucidate the neuroendocrine mechanisms that regulate testicular function in a representative primate, the rhesus monkey. Since many of the control systems that govern reproductive processes in mammals exhibit marked species differences, it is to be anticipated that studies of the reproductive physiology of non-human primates may have direct relevance to our understanding of the control of human fertility, and to treatment of reproductive diseases in man. The aim of the present proposal is to conclude our studies, at the organismic level of the negative feedback regulation of the secretion of pituitary L H and FSH. Particular attention will be paid to the role of testicular peptides, most notably inhibin, in the regulation of FSH secretion. For this purpose, passive immunization with antisera raised in sheep to a synthetic fragment of the gamma-subunit of human inhibin will be used. In addition a model for the regulation of gonadotropin secretion in the monkey, which has evolved as a result of our earlier work, will be rigorously tested. The hypophysiotropic clamp preparation, in which the drive to the pituitary gonadotroph is provided by an invariant iv GnRH infusion, will be used extensively in the experiments described in this proposal. For this purpose, monkeys will be implanted with indwelling venous catheters, fitted with nylon jackets, circulation with minimal restraint and without tranquilization. Most of the RIAs and bioassays to be employed in the proposal are standard procedures and have been in operation in the this laboratory for several years. Inhibin in plasma will be estimated by RIA using an antisera to a synthetic fragment of porcine gamma-inhibin. Surgical procedures will be conducted using standard aseptic technique with appropriate anesthesia and postsurgical analgesia.